1. Field of the Invention
This invention relates to the treatment of hop solids which is the residue remaining after liquid or supercritical CO2 extraction, and produces a hop product which imparts not only hop flavor and mouthfeel indistinguishable from original whole hops, but also provides light stability and flavor variations in malt beverages. Such treated hop solids can contribute hop flavor and mouthfeel to beer with low bitterness. However, a residual amount of alpha/iso-alpha-acids, which causes light instability in finished malt beverages, is still present in the hop solids. The present invention is directed to the preparation of light stable hop products, containing little or no alpha/iso-alpha-acid, for providing hop flavor and character for beer products which may be packaged in flint, clear, or green bottles.
2. Description of the Related Art
Hops, in the form of either the ground dried plant or pellets, are used in brewing to give malt beverages such as beer or ale their essential characteristics of aroma, flavor, mouthfeel, and bitterness, as well as contributing foam and anti-microbial activity to the brew. The hops are usually added to the boiling wort in the brewing kettle, and then fermented by yeast to produce the finished product. During boiling, alpha-acids in the hops are converted into iso-alpha-acids, which contribute the bitterness and foam in the finished product. Such iso-alpha-acids are, however, susceptible to a photochemical reaction which produces “skunk”, an undesirable sulfur flavor characteristic resulting from the presence of 3-methyl-2-butene-1-thiol. This reaction is known to occur when the finished product is packaged in flint or green bottles and exposed to light.
Hops may be separated into hop soft resins, i.e. CO2 hop extract (containing the extracted alpha-acids, beta-acids, and hop oil fraction or HOF), and hop solids, by employing liquid/supercritical CO2 or less-polar organic solvent extractions. The CO2 hop extract contributes most of the bitterness flavor in beer. Beer brewed solely with the CO2 hop extract does not impart a complete hops flavor spectrum to the beer due to the absence of the water-soluble components, which apparently remain in the hop solids. The bitterness flavor can also be added as pure forms after fermentation or in the finished products. To integrate the full spectrum of hop flavor would thus require the addition of hop solids to the brew, but the hop solids have been found to contain trace amounts of alpha/iso-alpha-acids, which, due to lack of light stability, contribute to skunkiness in beer. Therefore, to obtain the full flavor of the hops while avoiding skunkiness in beer, light stable hops would be of value.
It is known that there are a number of U.S. patents relative to this matter, such as Ting et al. U.S. Pat. No. 5,783,235, which teaches the preparation of a hop flavored, less bitter fermented beverage by addition of the solid hop residue remaining after CO2 extraction (as the sole hopping agent) to the wort, boiling the mixture, removing the solids from the fermented mixture, and fermenting the remainder to obtain the final product. While this method does provide a brew having less bitterness but a comparable hop flavor to a brew prepared using whole hops, it does not fully address the issue of iso-alpha-acids present in the solid hop residue. In a preferred embodiment of the Ting et al. '235 method, the solid hop residue and the hop oil fraction (HOF), which is the residue of a hop extract remaining after removal of alpha-acids and beta-acids from the hop extract obtained from the CO2 extraction, are pelletized and added to the wort prior to or during boiling. After the mixture is boiled and fermented with yeast to convert the hop components and the wort, the solids are then separated to obtain the liquid product. Since the solid hop residue is present in the brewing kettle, iso-alpha-acids are present in the final brew, potentially leading to an undesirable skunk flavor.
Ting et al., in U.S. Pat. No. 5,767,319, teach conversion of iso-alpha-acids to light stable tetrahydroiso-alpha-acids, which are known bittering agents. While an improvement over previous conversion methods, the patent necessitates additional treatment steps to obtain specified metal salts of the iso-alpha-acids, dissolving the metal salts in an aqueous alcohol medium, and reducing the iso-alpha-acids by hydrogenation under specific conditions to form the tetrahydroiso-alpha-acids, which are then recovered from the reaction medium. Such a method clearly adds complexity to the desired goal of providing a light stable form of hops.
In addition, Ting et al. teach, in U.S. Pat. No. 6,020,019, a method for the hydrogenation of hop soft resins, wherein carbon dioxide is used as a reaction solvent, in liquid or supercritical fluid form, for the conversion of iso-alpha-acids or beta-acids to tetrahydroiso-alpha-acids (tetrahydroisohumulones), preferably using an acidic lower alcohol to act as a promoter for the beta-acids. As previously indicated, tetrahydroiso-alpha-acids are known light-stable FDA-approved bittering agents which may be used to add hop flavoring to beer. In this patent, it was noted that the tetrahydroiso-alpha-acids were previously generally not made from the alpha-acids for economical reasons. The hydrogenation method of this patent permits the use of alpha-acids as a source of tetrahydroiso-alpha-acid for use in brewing.
Additional patents to Ting et al. include U.S. Pat. Nos. 5,523,489, 5,874,633, and 5,917,093. In these patents, methods for the preparation and/or purification of tetrahydroiso-alpha-acids (tetrahydroisohumulones) are discussed. In U.S. Pat. No. 5,523,489, tetrahydroisohumulones are prepared from isohumulones by hydrogenation in ethanol. In U.S. Pat. No. 5,917,093, alpha-acids and beta-acids present in the hop oil fraction of CO2 Hop Extracts are purified by mixing with an absorbent to remove catalyst poisons, thereby reducing the amount of catalyst necessary for hydrogenation to tetrahydroiso-alpha-acids and tetrahydrodesoxy-alpha-acids. In U.S. Pat. No. 5,874,633, patentees teach a method of hydrogenating and formulating a starting solution of iso-alpha-acids to obtain concentrated solutions of tetrahydroiso-alpha-acids.
In U.S. Pat. No. 5,972,411, Goldstein et al. teach the isolation and characterization of a group of odorless and non-volatile glycosides from extracted hops (hop solids which have previously been extracted with liquid/supercritical CO2 or less-polar solvents.) These glycosides are water soluble and consist of a group of aromatic compounds conjugated to mono-, di- and tri-saccharides. These glycosides are responsible for the formation of kettle hop flavor. Through both chemical and biological transformations, an essence and flavorant can be prepared for addition to an unhopped beer. These kettle hop flavor essences and flavorants provide economy, consistency, flexibility, quality and convenience to the brewing process because only one unhopped wort is required to brew a stock of unhopped beer, which can then be dosed with the desired amount of kettle hop flavor essence and flavorant.
In U.S. Pat. Nos. 5,013,571 and 5,013,572, Hay teaches methods for converting alpha acids to hop bittering flavors by exposing the alpha acids to an environment capable of isomerizing and reducing the alpha acids to form either tetrahydroiso-alpha-acids or hexahydroiso-alpha acids, and then steam stripping odor forming impurities from such to produce purified light stable hop bittering compounds.
In addition to the above, U.S. Pat. No. 4,002,683, of Todd, Jr., teaches a process for isomerizing alpha acids to iso-alpha-acids by contact with an aqueous solution of a metal ion to form materials suitable for use as bittering additives, wherein a water-immiscible organic solvent in which the alpha acid is soluble is employed. Todd, Jr., also teaches, in U.S. Pat. No. 4,666,731, the separation of the constituents of CO2 Hop Extracts employing aqueous alkali, followed by conversion of the separated alpha acid fraction into an iso-alpha acid or isohumulone fraction useful in the bittering of beer. Moreover, Todd, Jr. et al. teach, in U.S. Pat. Nos. 4,778,691 and 4,956,195, the removal of odor-forming impurities from hop flavors by extracting into water at a pH above 5, and separating the aqueous phase containing the impurities from the purified hop flavors, to recover a flavoring agent selected from unreduced and reduced alpha acids and iso-alpha-acids which is essentially odor-causing-impurity free. And, in U.S. Pat. No. 5,073,396, Todd, Jr. teaches the use of a non-acidic hop flavor fraction for production of beer, wherein the hop flavor fraction is made from CO2 hop extract to provide an extract essentially devoid of alpha and beta acids, by fractionation of the hop extract with an alkaline solution within controlled pH ranges. In U.S. Pat. No. 5,296,637, Stegink et al. teach production of odor-free tetrahydroisohumulates from alpha acids via the tetrahydrohumulates and subsequent isomerization.
Thus, there are a number of processes for the preparation, separation, purification, and use of hop bittering flavors for beer. However, a method for the production of light stable hops containing little or no alpha/iso-alpha-acids, which also imparts hop aroma and flavor to the brewing of beer equivalent to or comparable to the aroma and flavor attained from the use of conventional hops, has not previously been provided.